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How optical illusions trick your brain - Nathan S. Jacobs

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Optical illusions are images that seem to trick our minds into seeing
something different from what they actually are. But how do they work?
Nathan S. Jacobs walks us through a few common optical illusions and
explains what these tricks of the eye can tell us about how our brains
assemble visual information into the 3D world we see around us.

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Meet The Creators

Educator Nathan S. Jacobs

Director Biljana Labovic

Animator Lisa LaBracio

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Together,
all of the pieces of our visual system work together to rapidly create a 3D
rendering of our surrounding environment. But just like detecting edges in the retina or creating 3D surfaces from
gradients of light in the neocortex, we don’t see everything around us equally.
We focus on what’s most important to us.We focus on faces or animals that might kill us and consume us.

For
example, in the ‘what’ pathway there is a cortical region called the fusiform
face area that is specifically designed to help us see faces. In analogous cortical areas in monkeys
(inferotemporal cortex) there are cells that respond to facial features such as
how far apart the eyes are, how big the mouth is, and how curved and angry the
eyebrows look. There are cells that
respond to what direction the head is faced. All of this requires many
assumptions, one of which is that people aren’t upside down.

The
upside down face illusion is based on 1) the assumption that faces are usually
right side up, and 2) that different parts of the face are processed
separately. The upside down face has the
eyes and mouth cut out and turned upside down (or rights side up, I guess).
Then when the image is rotated the eyes and mouth get turned upside down and
the whole face looks weird.

So at every level, whether it’s the
retina or the neocortex, the neurobiological basis of optical illusions
demonstrates how our visual system translates confusing ambiguous light
patterns into realistic 3D objects around us.It does this by making assumptions, and then sticking to those
assumptions for better or worse. It gets
things wrong every once in awhile (for example, if you go out of your way to
make an optical illusion), but 99.9% of the time it gets it right and it does
so in less than 300 ms. Optical illusions don’t show us quirks in the visual
system, they provide a glimpse at the complex neurobiological systems required
to turn squiggly, smudgy dots captured by the retina into a realistic, animated
3D world around us.

However, rats “see” their surrounding environment by touching it with dozens of whiskers that they can move around to touch nearby objects. So we use our eyes to see, but rats use their whiskers and their sense of touch to see.
Now imagine that you and your pet rat are just hanging out when you see a marble on the ground. You look at the marble with your eyes and your pet rat looks at the marble by touching it with his whiskers. What are some things that both of you “see” even though you are using two totally different senses? What are some things that only you can see? What are some things that only your pet rat can see?

About TED-Ed Originals

TED-Ed Original lessons feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed original? Nominate yourself here »